The purpose of this research project is to analyze the afferent and efferent anatomical connections of discrete regions of the hypothalamus of the rat, concentrating on the afferent and efferent connections of discrete nuclei and regions of the medial basal hypothalamus. Particular emphasis will be placed on determining intrahypothalamic connections. Studies of the anatomical connections of the hypothalamus have been hindered by limitations in anatomical technique. However, recent developments in anatomical methodology offer promise for a systematic and comprehensive analysis of the hypothalamic connections, especially for determining intrahypothalamic connections. The anatomical connections of a number of discrete hypothalamic regions will be determined with a newly developed horseradish peroxidase (HRP) method and with the autoradiographic method. The HRP method to be used has been developed in this laboratory and offers several advantages over other methods currently available. Fluorescein isothiocyanate-conjugated HRP is deposited microelectrophoretically and a sensitive histochemical procedure is used to detect the HRP. Detectable transport occurs from deposits 125 um in diameter and there is little secondary diffusion of the enzyme. This method will be used to examine the afferent connections of a number of discrete regions of the medial basal hypothalamus. The autoradiographic method to be used is based on microelectrophoretic delivery of radiolabeled amino acids. This method will provide greater localization within the hypothalamus than has been achieved previously. The emphasis of the autoradiographic studies will be to confirm and extend findings made with the modified HRP method. The proposed research will add to what is known about the anatomical organization of the hypothalamus, especially to what is known about intrinsic connections. This information will be useful not only in understanding anatomical connections in the strictest sense, but would also provide a framework for interpreting information obtained with other methods, such as biochemical and immunohistochemical studies.